Mix all the ingredients together. Form into a prepared tin - an 8x8" should work well and bake at 350F for 10 minutes.
Once out of the oven, using the base of another pan, press down to ensure as thin as possible.
Allow to cool.
For the filling
Melt the peanut butter and butter together, either on the stove top or in the microwave. Add in the vanilla and icing sugar and mix really well. Spread on top of the crust and set aside while preparing the topping.
For the topping
Melt the chocolate and peanut butter together and mix to ensure all is smooth. Spread on top of the filling and chill in a refrigerator for at least 1 hour.
Once chilled and the chocolate topping has hardened, cut into pieces.